1. Field of the Invention
The present invention relates to an electric vehicle configured to be driven by a motor using a battery unit as a power source.
2. Description of the Related Art
A battery unit used in an electric vehicle includes a battery module composed of a plurality of cells, a battery case that contains the battery module, etc. The battery case is provided with, for example, a tray member that supports the battery module, a cover member that covers the top of the tray member, etc. Cells are secondary batteries, such as lithium-ion batteries.
A structure has been made to reduce damage to a vehicle body and a battery unit in case of a collision of an electric vehicle that is provided with the battery unit. An automobile described in Jpn. Pat. Appln. KOKAI Publication No. 6-270694, for example, is configured so that a battery carrier moves to a position below the vehicle body when subjected to a frontal impact force. Collision energy can be absorbed by this configuration.
An electric vehicle is provided with a large battery unit in its body to maximize its mileage. Accordingly, the battery unit occupies a rather large area of the floor section of the vehicle body as viewed from above the body. In some cases, the large battery unit may be located covering, for example, the entire width of the vehicle body.
With respect to the longitudinal direction of the vehicle body, a relatively large crush zone can be secured ranging from the front end of the vehicle body to that of the battery unit. Further, a relatively long distance can be secured from the rear end of the battery unit to that of the vehicle body. The vehicle body structure of this type can relatively easily absorb a collision load that acts on the battery unit in case of a head-on or rear-end collision.
With respect to the width direction of the vehicle body, however, the distance from a side surface of the battery unit to that of the vehicle body is short. Accordingly, it is hard to secure a crush zone large enough to absorb energy from a collision load that is applied sideways. In case of a side collision, therefore, a collision load may act directly on the battery unit to damage the cells with higher possibility than in the case of a head-on or rear-end collision. The damaged cells are supposed to cause an internal short circuit between electrodes and heat generation with high probability.